Reciprocating cutting blades, often referred to as sickle sections, are commonly used in machines that cut forage (e.g., for cattle feed) and that cut grain (e.g., prior to thrashing to collect the seed). Other uses include tea leaf harvesting and landscaping applications, such as hedge trimming. Even some underwater weed cutters utilize similar sickle section configurations. The sickle sections are typically triangular-shaped knives having two sharpened edges. The sharpened edges are often also serrated to improve cutting performance. A plurality of sickle sections is attached to a cutter bar that oscillates or reciprocates back and forth in a direction substantially perpendicular to the cutting path through the crop. The cutter bar and the attached sickle sections are typically mounted for oscillation near the base of the crop stems, just above the ground. The sickle sections cooperate with a stationary blade, called a guard, to create a shearing action that cuts the crop.
Sickle sections are subject to wear by the fibrous stalks of the crop being cut, sand, and other abrasive materials carried into the sections during cutting. Increasing the hardness of the sickle sections improves resistance to wear due to normal cutting conditions. However, increasing the hardness of the sickle section also tends to increase the brittleness of the section and reduces the capacity of the knife to withstand cracking under impact forces created by foreign objects encountered by the section. Even though the guards substantially prevent the intrusion of most large objects, some will inevitably get through and impact the knife with loads high enough to cause cracking and/or breakage.
Furthermore, the cutting edges are also subject to deformation by smaller pebbles, rocks, and other debris. This deformation has the effect of dulling the cutting edges without necessarily removing material from the blade. Dull cutting edges may be perceived as having been worn dull. Also, dull cutting edges do not cut the stalks as cleanly, thereby reducing the quality of cut.
One way of manufacturing a sickle section to meet the various design criteria is to treat the section after it is formed. It is commonly known to harden a sickle section using a variety of methods. One such method is to induction harden the material along the two cutting edges of the section. Such induction hardening processes, using a high-carbon, spring grade of steel (e.g., 1074 annealed steel), can result in a hardened area along the cutting edges having a hardness of about 50-55 Rc.
For cutting under more hostile conditions, it has been known to dip or otherwise coat the previously induction-hardened sickle section in a chromium solution to plate the entire sickle section. In addition to improved corrosion resistance, the hard chrome plating provides a hard skin that further improves the toughness at the cutting edges.
Another known method of hardening sickle sections is through austempering. Austempered sickle sections will typically have a hardness of about 48-52 Rc through the entire blade.